What is the theoretical probability that a coin toss results in two tails showing?

Which is the equation of a line perpendicular to the line with the equation 3x+4y=8

Two cyclists 84 miles apart start riding toward each other at the samen time. one cycles 2 times as fast as the other. if they meet 4 hours later what is the speed (in miles) of the faster cyclists

An airplane travels at an unknown elevation before it descends 3 miles to an elevation of 15 miles. find the elevation of the plane before its descen.